Method and system for encapsulating time division multiplex data into individual packets of a packet based network

ABSTRACT

A method of encapsulating TDM data into individual data packets for transmission across a packet network includes delineating the TDM data into one or more signaling multiframes, wherein each signaling multiframe includes one period of a periodic signaling pattern. The method also includes appending a header that is associated with the individual data packets to each of the signaling multiframes of TDM data. Further, a method of selecting the number of multiframes of TDM data in the data packet includes calculating the efficiency of the data packet as a function of the number of multiframes, and selecting the number of multiframes so that the efficiency of the data packet increases exponentially as a number of time-slots in the TDM data increases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following U.S. applications, ofcommon assignee, from which priority is claimed, and the contents ofwhich are incorporated herein in their entirety by reference:

“Method And System For Encapsulating Time Division Multiplex Data IntoReal Time Protocol Packets For Transport,” U.S. Provisional PatentApplication Ser. No. 60/353,615, filed Feb. 1, 2002.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable

REFERENCE TO MICROFICHE APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to digital communications, and moreparticularly, to methods and systems for transporting time divisionmultiplex (TDM) data via packet-based networks.

TDM data may consist of Constant Bit Rate (CBR) data as well as non-CBRdata. CBR data includes real-time data such as voice, video orprofessional, studio quality (i.e., program) audio. Typically, constantbit rate (CBR) data is formatted into 64 kbps time-slots (TS) and TDMtechniques are used to map the time-slots into T1 or E1 frames which aretransported over the Public Switched Telephone Network (PSTN).

In one “real world” example of CBR data, the program audio produced in astudio must be relayed to a remote transmitter site for subsequentbroadcast. In some cases, a studio-to-transmitter link (hereinafterreferred to as STL) may be implemented with a T1 (or E1) digital circuitvia the PSTN. In prior art, this digital circuit is typicallyimplemented using expensive “nailed up” (i.e., dedicated) T1 lines. Oneway to reduce the cost of such an STL is to relay the professionalquality audio data over an existing, general purpose packet basednetwork such as the Internet. Other formats of CBR data that wouldnormally be transmitted via a dedicated T1 line (e.g., MPEG, APT-X,Linear etc.) also could be advantageously transported via a packet basednetwork. A unique “convergence layer,” i.e., a set of rules that defineshow to encapsulate the T1/E1 data into the individual packets of thepacket based network, must be specifically designed for each particularmedia type. Thus, each individual convergence layer is media-specific.Further, more generic types of data, such as voice, video, synchronousdata, asynchronous data, etc., could also benefit by being transportedover packet networks.

A disadvantage of prior art systems for encapsulating T1 or E1 TDM-baseddata into a packet based communications protocol is the requirement forunique convergence layers for each data type. Further, prior arttechniques for encapsulating T1 or E1 data into a packet based protocoltypically encapsulate all of the T1 overhead bits, as well as thepayload data, which reduces the overall bandwidth efficiency.

SUMMARY OF THE INVENTION

In one aspect, the invention comprises a method of encapsulating TDMdata into individual data packets for transmission across a packetnetwork. The method includes delineating the TDM data into one or moresignaling multiframes, wherein each signaling multiframe includes oneperiod of a periodic signaling pattern. The method further includesappending a header that is associated with the individual data packetsto each of the signaling multiframes of TDM data.

An embodiment of the method further includes delineating the TDM datasuch that a first byte in the one or more signaling multiframes isdirectly adjacent to the header.

Another embodiment of the method further includes appending an RTPheader to each of the signaling multiframes.

Another embodiment of the method further includes appending a modifiedRTP header to each of the signaling multiframes.

Another embodiment of the method further includes extracting the TDMdata from one or more time-slots from a TDM data stream.

Another aspect of the invention comprises a data packet constructed andarranged to encapsulate TDM data for transmission over a packet network.The data packet includes a segment of the TDM data from one or more TDMtime-slots. The segment of the TDM data corresponds to a signalingmultiframe of the TDM data that includes one period of a periodicsignaling pattern. The data packet further includes a header associatedwith the individual data packets appended to the segment of the TDMdata.

In another embodiment of the data packet, the TDM data includes T1 data.

In another embodiment of the data packet, the TDM data includes E1 data.

In another embodiment of the data packet, the segment of TDM data isdelineated such that a first byte in the signaling multiframe isdirectly adjacent to the header. The header may include an RTP header.Further, the RTP header may include an extended RTP header that containsdata associated with (i) the starting time-slot, (ii) the number oftime-slots per frame, and (iii) the number of multiframes in the datapacket.

In another embodiment of the data packet, the signaling multiframecorresponds to a multiframe associated with the TDM data. The multiframemay includes 16 frames for E1 data, or the multiframe may include 24frames for T1 data.

Another aspect of the invention comprises a method of selecting a valueof a parameter k, wherein the parameter k represents a number ofmultiframes of TDM data in a data packet for transmission across apacket network, and the packet includes packet payload data and packetoverhead data. The method includes calculating one or more values of theparameter k as a function of one or more input parameters. Each value ofk corresponds to n, a number of time-slots in the TDM data, such thatthe efficiency of the data packet increases exponentially as the numberof time-slots in the TDM data increases. The method further includesselecting a value of the parameter k corresponding to the inputparameters associated with the payload data and the overhead data.

In another embodiment, the method further includes calculating theparameter k such that

${k = {{Ceiling}\left\lbrack \frac{- {{OH}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{MN}_{mx}{\mathbb{e}}^{n/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)}}{{nM}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} - {OH\mathbb{e}}^{n/\tau} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)} \right\rbrack}},$wherein

OH represents an amount of packet overhead data;

M represents an amount of frames in a signaling multiframe of the TDMdata;

N_(mx) represents a maximum amount of times slots per frame associatedwith the TDM data;

τ represents a time constant;

n represents an amount of time-slots associated with the TDM data;

EF₁ represents a minimum allowed efficiency of the data packet;

and Ceiling[ ] represents a function for limiting the parameter k to aninteger value.

In another embodiment, the method further includes delineating the TDMdata such that a first byte in the one or more signaling multiframes isdirectly adjacent to the header.

In another embodiment, the method further includes appending an RTPheader to each of the signaling multiframes.

In another embodiment, the method further includes appending a modifiedRTP header to each of the signaling multiframes.

In another embodiment, the method further includes extracting the TDMdata from one or more time-slots from a TDM data stream.

Another aspect of the invention comprises a system for compiling one ormore data packets for transmission across a packet network. Each packetincludes packet payload data and packet overhead data. A parameter kdescribes the number of multiframes of TDM data in each data packet, anda parameter n describes a number of time-slots in the TDM data. Thesystem includes a processor for calculating one or more values of theparameter k as a function of one or more input parameters, such thateach value of k corresponds to a value of n, and the efficiency of thedata packet increases exponentially as n increases. The processorfurther selects a particular value of the parameter k, corresponding tothe input parameters associated with the payload data and the overheaddata. The system also includes a packet assembler for receiving datafrom one or more TDM time-slots, along with the parameter k and one ormore of the input parameters, and producing one or more data packetseach having k multiframes of TDM data.

In another embodiment, the processor calculates the parameter k suchthat

${k = {{Ceiling}\left\lbrack \frac{- {{OH}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{MN}_{mx}{\mathbb{e}}^{n/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)}}{{nM}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} - {OH\mathbb{e}}^{n/\tau} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)} \right\rbrack}},$the input parameters include OH, M, N_(mx), τ, n, EF₁, and

OH represents an amount of packet overhead data;

M represents an amount of frames in a signaling multiframe of the TDMdata;

N_(mx) represents a maximum amount of times slots per frame associatedwith the TDM data;

τ represents a time constant;

n represents an amount of time-slots associated with the TDM data;

EF₁ represents a minimum allowed efficiency of the data packet;

and Ceiling[ ] represents a function for limiting the parameter k to aninteger value.

In another embodiment of the system, the TDM data includes T1 data.

In another embodiment of the system, the TDM data includes E1 data.

In another embodiment of the system, the data packet includes a header,and the TDM data is delineated such that a first byte in a signalingmultiframe is directly adjacent to the header.

In another embodiment of the system, the header includes an RTP header.

In another embodiment of the system, the RTP header includes an extendedRTP header having data associated with (i) starting time-slot, (ii)number of time-slots per frame, and (iii) number of multiframes in thedata packet.

In another embodiment of the system, the signaling multiframecorresponds to a multiframe associated with the TDM data

In another embodiment of the system, the multiframe includes 16 framesfor E1 data.

In another embodiment of the system, the multiframe includes 24 framesfor T1 data.

Another embodiment of the system further includes a switch for receivingthree inputs: (i) the parameter k from the processor, (ii) auser-defined parameter k, and (iii) a switch control signal. The switchprovides, to the packet assembler, either the parameter k from theprocessor or the user-defined parameter k, depending upon the state ofthe switch control signal.

BRIEF DESCRIPTION OF DRAWINGS

The various unique features, as well as various inventive embodiments,may be more fully understood from the following description, when readtogether with the accompanying drawings in which:

FIG. 1 shows how TDM data is encapsulated into Real Time Protocolpackets, according to the present invention;

FIG. 2 shows E1 frame configuration as used in the data encapsulation inFIG. 1;

FIG. 3A shows T1 frame configuration (16 state signaling) as used in thedata encapsulation in FIG. 1;

FIG. 3B shows T1 frame configuration (4 state signaling) as used in thedata encapsulation in FIG. 1;

FIG. 4 shows the RTPx header extension as used in the data encapsulationin FIG. 1;

FIG. 5 shows how the efficiency EF varies as a function of n, and howthe time constant τ controls the rate at which the efficiency changes;

FIG. 6 shows k, the number of multiframes encapsulated in an RTP packetaccording to the present invention, plotted as a function of n;

FIG. 7 plots k of FIG. 6 along with several other associated parameters;

FIG. 8 plots the parameters k, PL and EFF vs. n with the efficiencyfloor EF1=0.8;

FIG. 9 plots the parameters k, PL and EFF vs. n with τ=6, and all otherparameters the same as for FIG. 7; and,

FIG. 10 shows the parameter k, the number of multiframes encapsulated inan RTP packet according to the present invention, in tabular form.

FIG. 11 is a block diagram showing an embodiment of a system accordingto the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method of encapsulating TDM data into individual data packets (alsoreferred to as “the convergence layer”), as described herein, provides anovel way to transport T1 or E1 data via existing packet based networks.Thus, the method described herein is a set of rules that defines how toorganize TDM data into the individual packets of a packet basedcommunications protocol. Other classes of TDM data, such as FractionalT1/E1 and N×64K, may also be transported using the method describedherein. For the purposes of illustration and example only, thedescription of the method herein concentrates on the transport of T1 orE1 data (referred to as E1/T1 herein). The underlying concepts taughtare also applicable to other data formats. The present method ofencapsulating TDM data into individual data packets (i.e., theconvergence layer) allows TDM data, for example T1, E1, N×64k, etc., tobe encapsulated into Real Time Protocol (referred to herein as “RTP”)packets, as shown in FIG. 1. Each frame 102 is distributed among ntime-slots 104, and M frames form each multiframe 106. For transportingreal-time CBR applications over packet networks, the protocol most oftenused is RTP, which provides additional end-to-end delivery servicesneeded by upper layer protocols to transport data with real-timecharacteristics, such as audio, video and voice. Those services includepayload type identification; sequence numbering, time stamping anddelivery monitoring. The sequence numbers included in RTP allows thereceiver to reconstruct the sender's packet sequence.

For IP based networks RTP typically runs on top of UDP to make use ofits multiplexing and checksum services. This is denoted by RTP/IP/UDP toindicate the protocol layers involved.

For Frame Relay based networks RTP runs on top of the Frame Relayprotocol and is denoted by FR/RTP. It is also possible to encapsulatethe RTP/IP/UDP inside the Frame Relay packet, which becomesFR/IP/UDP/RTP.

In addition to the standard headers for IP, UDP and FR we add afour-byte header for the convergence layer. This four-byte header isreferred to the RTP extension header (RTPx).

The number of T1/E1 multi-frames in a single RTP packet is given by theparameter k. The value of k can be manually selected or automaticallydetermined by an Exponential Weighting Algorithm (EWA). The EWA isdescribed in more detail herein.

A T1/E1 multiframe (referred to herein as “MF”) consists of M frames,where M is equal to 24 for T1 and M is equal to 16 for E1. Each frameconsists of n DS0 time-slots, where the value of n can be from 1 to 24for T1 and 1 to 32 for E1. The parameter n is also referred to herein asthe “time-slot utilization.” The T1/E1 framing bits are not encapsulatedin the RTP packets, and are thus discarded in the convergence layer.

Channel Associated Signaling (referred to herein as “CAS”), also knownin the art as ABCD or AB signaling, is typically used to implement voicetrunking over T1/E1. CAS is essentially a periodic signaling patternwithin the E1/T1 data stream. In order to preserve the signalinginformation after the T1/E1 framing bits are discarded, the convergencelayer requires that the first byte following the RTP header must be thefirst byte in an E1/T1 signaling multiframe (referred to herein as“SMF”). For 16-state signaling the ABCD signaling bits repeat once permultiframe (i.e., every M frames). Therefore the length of the SMF isthe same as the length of the T1/E1 multiframe. The SMF for 16-statesignaling is 16 frames in length for E1 and 24 frames for T1. The firstframe in an SMF for 16-state signaling corresponds to frame-0 for E1(see FIG. 2) and frame-1 for T1 (see FIG. 3). This positioning of theT1/E1 frames within the SMF allows CAS signaling bits to be identifiedand extracted at the remote end. The ABCD signaling bits can thus betransported transparently to the upper layers without having to send theT1/E1 framing bits. For 4-state (AB) CAS signaling only two signalingbits are used. The SMF for E1 is the same as for the 16-state case. ForT1 however, the AB bits are repeated every M/2 frames. Therefore the SMFis only 12 frames long. The first byte following the RTP header for thiscase is either the first byte in frame 1 or frame 13. The E1 signalingbyte is transported transparently in time-slot 16 (TS-16). For E1, TS-0is not used. Therefore in one preferred embodiment, TS-16 in the E1payload is transported in TS-0 of the encapsulated payload. In otherembodiments, TS-16 from the E1 payload is conveyed in TS-16 of theencapsulated payload. For T1 the CAS signaling is embedded in the TDMdata (LSB) and is transparent to the upper layers. The convergence layerfor N×64 has no requirement to maintain multi-frame boundaries, so M(i.e., the length of the SMF) can be any value.

The convergence layer defines a modified RTP header that includes afour-byte extension, denoted by RTPx, as shown in FIG. 4, where thefollowing RTPx fields are defined as follows:

a) Start TS 5 bits, starting Time-Slot for T1/E1 payload. b) n 5 bits,Number of time-slots used in the T1/E1 frame c) k 6 bits, Number ofmulti-frames encapsulated in an RTP packet d) Spare 16 bits, Undefined.These are optional and may be used for such things as a user data linkor for additional payload type information.

The convergence layer requires that the IP packet after encapsulationshall be less than or equal to 1500 bytes, which is the MaximumTransmission Unit (MTU) of Ethernet. This is done in order to avoidfragmenting packets resulting in error multiplication.

A number of parameters may be defined associated with the convergencelayer described herein. For example:

-   1) Packet Overhead—this parameter describes the number of bytes in    each packet for various communication layers.    -   Packet Overhead=20 for IP    -   Packet Overhead=8 for UDP    -   Packet Overhead=12 for RTP    -   Packet Overhead=8 for Frame Relay    -   Packet Overhead=4 for RTPx (RTP Extension)-   2) OH—this parameter describes the total number of overhead bytes    for various combinations of communications layers.    -   OH=44 . . . for IP/UDP/RTP/RTPx    -   OH=24 . . . for FR//RTP/RTPx-   3) n—this parameter describes the number of time-slots per T1/E1    frame.    -   n=1 to 31 . . . for E1    -   n=1 to 24 . . . for T1-   4) M—this parameter describes the number of frames in a Signaling    Multiframe.    -   M=16 . . . for E1    -   M=24 . . . for T1 with 16-state signaling    -   M=12 . . . for T1 with 4-state signaling-   5) N_(mx)—this parameter describes the maximum number of time-slots    per frame    -   N_(mx)=31 . . . for E1    -   N_(mx)=24 . . . for T1-   6) k—this parameter describes the number of Multi-frames in a packet    -   Manually select k for k<32    -   Automatically select k based on n use weighting factor algorithm-   7) T_(MF)—this parameter describes the period (duration) of a    Signaling Multiframe (SMF)    -   T_(MF)=2 msec . . . for E1    -   T_(MF)=3 msec . . . for T1 with 16-state signaling    -   T_(MF)=1.5 msec . . . for T1 with 4-state signaling-   8) PL—this parameter describes the size of the payload in bytes;    PL=k n M-   9) PKT—this parameter describes the size of each packet in bytes,    including overhead and payload.    -   PKT=PL+OH-   10) EF—this parameter, the Packet Efficiency, describes the ratio of    the payload size to the overall size of the packet.    -   EF=PL/PKT-   11) T_(D)—this parameter, the packet latency, describes the duration    of the total number of multiframes in a packet.    -   T_(D)=k T_(MF) msec

In one embodiment, the number of T1/E1 multiframes in a single RTPpacket (i.e., the parameter k) is selected manually, in cases for whichthe user needs to control or minimize the latency. In this embodiment,the user specifies the time-slot utilization n, and the number ofmultiframes k to be encapsulated.

In another embodiment, the parameter k is selected automatically by anExponential Weighting Algorithm (hereinafter referred to as EWA), whichoptimizes the value of k for high EF and thus high bandwidth efficiency.In general, high bandwidth efficiency is more important for larger n,i.e., for a greater time-slot utilization of the T1/E1 transmission.Increasing the bandwidth efficiency requires increasing the value of k,i.e., increasing the number of multiframes to be encapsulated. Anincrease in packet latency may be an undesirable consequence ofincreasing k.

Note that for large values of n (i.e., high time-slot utilization), thevalue of k does not need to be large for high bandwidth efficiency. Forexample, given n=31 in an E1 system, a value of k=1 yields an efficiencythat is greater than 90% for the IP/UDP case. However, for small valuesof n, a large value of k may be required to achieve the same 90%, whichconsequently increases latency. This embodiment uses an algorithm (EWA)to control the percentage of packet overhead (with respect to the totalpacket) so as to exponentially weight the bandwidth efficiency. Forlower values of n, the EWA allows a larger percentage of packetoverhead, lowering the packet efficiency EF and thus the bandwidthefficiency. The EWA gradually decreases the percentage of the packetoverhead, so as to increase the packet efficiency EF, as n get larger. A“minimum allowed efficiency” may be established by applying apredetermined input parameter, EF₁, to the EWA, which occurs at n=1. Theuser can also specify an exponential time constant τ. The value of τdetermines how fast or slow the packet efficiency EF increases. In oneembodiment, values for τ range from 1 to 8, although other suitableranges for τ may also be used. Values of τ at or near the low end of theallowable range typically provide faster convergence. Details of the EWAare set forth via the following equations and text.

The payload size (PL) in bytes is the product of the number ofmultiframes sent (k), the number of frames in each multiframe (M), andthe number of DS0 time-slots in each frame (n), i.e.,PL=knM  (1)

The packet size PKT in bytes is the sum of the payload size (PL) and thetotal overhead bytes (OH) in each packet, i.e.,

$\begin{matrix}\begin{matrix}{{PKT} = {{OH} + {PL}}} \\{= {{knM} + {OH}}}\end{matrix} & (2)\end{matrix}$

The efficiency EFF as a function of n is given by the ratio of thepayload size (PL) to the overall packet size (PKT), i.e.,

$\begin{matrix}{{EFF} = {\frac{PL}{PKT} = \frac{knM}{{knM} + {OH}}}} & (3)\end{matrix}$

When the maximum number of DS0 time-slots are utilized (i.e., n=N_(mx)),the minimum efficiency E₃₁ occurs for k=1, and (for E1) is given by

$\begin{matrix}\begin{matrix}{E_{31} = {{EFF}\left( {\left. k\rightarrow 1 \right.,\left. n\rightarrow N_{\max} \right.} \right)}} \\{= \frac{{MN}_{\max}}{{MN}_{\max} + {OH}}}\end{matrix} & (4)\end{matrix}$

A weighted efficiency, EF, is given by the following equation:

$\begin{matrix}{{EF} = {{EF}_{31} - {\left( {{EF}_{31} - {EF}_{1}} \right){\mathbb{e}}^{\frac{1 - n}{\tau}}}}} & (5)\end{matrix}$

The weighted efficiency EF in equation (5) increases exponentially as napproaches N_(mx). The packing of each individual packet is based on thetarget overhead percentage that produces a minimum efficiency EF₁. Thisalgorithm of equation (5) uses an exponential weighting factor, suchthat the efficiency increases as the number of time-slots n increases,from a minimum of EF₁ at n=1, to a maximum of EF₃₁ at n=N_(max). FIG. 5shows how the efficiency EF varies as a function of n, as described byequation (5), and how the time constant τ controls the rate at which theefficiency changes. FIG. 5 shows two curves, one representing τ=2 andone representing τ=6. Although both curves have essentially the samevalue at the extremes of n (i.e., both begin at EF₁=0.7 and have a finalefficiency of approximately 0.9), the curve corresponding to τ=2approaches the 0.9 efficiency level with respect to n than the curvecorresponding to τ=6.

The expression for EFF given by equation (3) and the expression for EFgiven by (5) are both functions of n. Setting the expression for EFFequal to the expression for EF and solving for k yields:

$\begin{matrix}{\overset{\sim}{k} = \frac{\begin{matrix}{- {{OH}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{MN}_{mx}{\mathbb{e}}^{n/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{OH}\;{\mathbb{e}}^{1/\tau}}} \right)}}\end{matrix}}{{nM}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} - {OH\mathbb{e}}^{n/\tau} + {{EF}_{1}{OH}\;{\mathbb{e}}^{1/\tau}}} \right)}} & (6)\end{matrix}$

A quantizing function (referred to herein as “Ceiling[ ]”), which roundsthe argument within the brackets to the nearest integer, is applied tothe right side of equation (6). Equation (6) must be quantized becausethe variable k can only take on integer values. The resulting equationgiven by equation (7) below is referred to herein as the ExponentialWeighting Algorithm (EWA).

$\begin{matrix}{k = {{Ceiling}\begin{matrix}\left\lbrack \frac{- {{OH}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{MN}_{mx}{\mathbb{e}}^{n/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{OH}\;{\mathbb{e}}^{1/\tau}}} \right)}}{{nM}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} - {OH\mathbb{e}}^{n/\tau} + {{EF}_{1}{OH}\;{\mathbb{e}}^{1/\tau}}} \right)} \right\rbrack\end{matrix}}} & (7)\end{matrix}$

Using the value of k calculated from equation (7), the delay (i.e., thelatency) can be calculated as follows:T_(D)=kT_(MF)  (8)

FIG. 6 shows k from equation (7) plotted as a function of n. Theparameters used in this example (i.e., N_(max)=31, M=16, OH=44, and τ=2)are for E1 over IP/UDP/RTP, for efficiencies of EF=0.7 and 0.8.

FIG. 7 plots k, PL and EFF vs. n, as derived from equation (7). Some ofthe parameters were scaled in order to plot them all on the same graph.The payload PL is scaled down by a factor of 100 and the efficiency EFFis scaled up by a factor of 10. Thus, FIG. 7 plots k, PL/100 and 10 EFFfor EF1 of 60%. FIG. 7 shows that the payload PL is below an uppertarget limit (i.e., max PL) of 1500 bytes.

FIG. 8 also plots the parameters k, PL and EFF vs. n, as derived fromequation (7), with the same scaling that was used for FIG. 7. FIG. 8plots the parameters k, PL and EFF vs. n with the efficiency floorEF1=0.8, and all other parameters the same as for FIG. 7. Comparing FIG.7 to FIG. 8 therefore shows how the parameters k, PL and EFF vary withrespect to n for different minimum efficiencies.

FIG. 9 plots the parameters k, PL and EFF vs. n with τ=6, and all otherparameters the same as for FIG. 7. Comparing FIG. 7 to FIG. 9 thereforeshows the effect that τ has on convergence of the parameters k, PL andEFF.

FIG. 10 shows a selection of parameters produced from equation (7) intabular form (i.e., a “lookup table”) for E1 over IP/UDP/RTP withminimum efficiency of 90%, 80% and 70%, and parameters of N_(max)=31,M=16, OH=44, and τ=2. The lookup table of FIG. 10 may be used to providea suitable operating point for the packet protocol (i.e., a particularvalue of k with respect to n) given a desired efficiency EF andefficiency floor E₁.

One embodiment of a system 200 for implementing the EWA according toequation (7) (i.e., for selecting a value of k so as to exponentiallyweight the packet efficiency) is shown in block diagram form in FIG. 11.The system 200 includes a packet assembler 202, a processor 204, andswitch 206. The packet assembler 202 receives TDM data for encapsulationin packets. The processor 204 receives user input parameters 208 (e.g.,maximum time-slots per frame Nmx, overhead size OH, frames per signalingmultiframe M, minimum efficiency EF1, time constant τ, number oftime-slots associated with the TDM data n, et al.) to the processor 204.The processor 204 calculates a value of the parameter k as a function ofthe user input parameters 208. The processor 204 passes the parameter k,through the switch 206, to the packet assembler. Each possible value ofk that the processor 204 generates corresponds to one value of thenumber of time-slots n in the TDM data, such that the efficiency of thedata packet increases exponentially as the number of time-slots in theTDM data increases. Thus, the processor 204 provides values of k fordifferent values of n to the packet assembler 202, according the EWA asdescribed herein, and the packet assembler 202 compiles packets withdesired efficiencies, according to the EWA. The user can also provide a“manual” setting of k to the packet assembler 202 via the switch 206, soas to bypass the EWA. To manually select k, the user provides a manual kvalue to the switch 206 and provides an appropriate control signal 208to the switch so that the manual value of k is presented to the packetassembler 202, rather than the k generated by the EWA.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of the equivalency ofthe claims are therefore intended to be embraced therein.

1. A method of selecting a value of a parameter k, wherein the parameterk represents a number of multiframes of TDM data in a data packet fortransmission across a packet network, and the packet includes packetpayload data and packet overhead data, comprising: calculating one ormore values of the parameter k as a function of one or more inputparameters, each value of k corresponding to n, a number of time-slotsin the TDM data, such that the efficiency of the data packet increasesexponentially as the number of time-slots in the TDM data increases;and, selecting a value of the parameter k corresponding to the inputparameters associated with the payload data and the overhead data.
 2. Amethod according to claim 1, further including calculating the parameterk such that${k = {{Ceiling}\left\lbrack \frac{- {{OH}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{MN}_{mx}{\mathbb{e}}^{n/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)}}{{nM}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} - {OH\mathbb{e}}^{n/\tau} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)} \right\rbrack}},$the input parameters including OH, M, N_(mx), τ, n, EF₁, wherein: OHrepresents an amount of packet overhead data; M represents an amount offrames in a signaling multiframe of the TDM data; N_(mx) represents amaximum amount of times slots per frame associated with the TDM data; τrepresents a time constant; n represents an amount of time-slotsassociated with the TDM data; EF₁ represents a minimum allowedefficiency of the data packet; and Ceiling[ ] represents a function forlimiting the parameter k to an integer value.
 3. A method according toclaim 1, further including delineating the TDM data such that a firstbyte in the one or more signaling multiframes is directly adjacent tothe header.
 4. A method according to claim 1, further includingappending an RTP header to each of the signaling multiframes.
 5. Amethod according to claim 4, further including appending a modified RTPheader to each of the signaling multiframes.
 6. A method according toclaim 1, further including extracting the TDM data from one or moretime-slots from a TDM data stream.
 7. A system for compiling one or moredata packets for transmission across a packet network, each packetincluding packet payload data and packet overhead data, wherein aparameter k describes the number of multiframes of TDM data in each datapacket, and a parameter n describes a number of time-slots in the TDMdata, comprising: a processor (i) for calculating one or more values ofthe parameter k as a function of one or more input parameters, such thateach value of k corresponds to a value of n, and the efficiency of thedata packet increases exponentially as n increases, and (ii) forselecting a particular value of the parameter k corresponding to theinput parameters associated with the payload data and the overhead data;a packet assembler for receiving data from one or more TDM time-slots,along with the parameter k and one or more of the input parameters, andproducing one or more data packets each having k multiframes of TDMdata.
 8. A system according to claim 7, wherein the processor calculatesthe parameter k such that${k = {{Ceiling}\left\lbrack \frac{- {{OH}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{MN}_{mx}{\mathbb{e}}^{n/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)}}{{nM}\left( {{{- {MN}_{mx}}{\mathbb{e}}^{1/\tau}} + {{EF}_{1}{MN}_{mx}{\mathbb{e}}^{1/\tau}} - {OH\mathbb{e}}^{n/\tau} + {{EF}_{1}{OH\mathbb{e}}^{1/\tau}}} \right)} \right\rbrack}},$the input parameters including OH, M, N_(mx), τ, n, EF₁, wherein: OHrepresents an amount of packet overhead data; M represents an amount offrames in a signaling multiframe of the TDM data; N_(mx) represents amaximum amount of times slots per frame associated with the TDM data; τrepresents a time constant; n represents an amount of time-slotsassociated with the TDM data; EF₁ represents a minimum allowedefficiency of the data packet; and Ceiling[ ] represents a function forlimiting the parameter k to an integer value.
 9. A system according toclaim 7, wherein the TDM data includes T1 data.
 10. A system accordingto claim 7 wherein the TDM data includes E1 data.
 11. A system accordingto claim 7, wherein the packet includes a header, and the TDM data isdelineated such that a first byte in a signaling multiframe is directlyadjacent to the header.
 12. A system according to claim 11, wherein theheader includes an RTP header.
 13. A system according to claim 12,wherein the RTP header includes an extended RTP header having dataassociated with (i) starting time-slot, (ii) number of time-slots perframe, and (iii) number of multiframes in the data packet.
 14. A systemaccording to claim 11, wherein the signaling multiframe corresponds to amultiframe associated with the TDM data.
 15. A system according to claim14, wherein the multiframe includes 16 frames for E1 data.
 16. A systemaccording to claim 14, wherein the multiframe includes 24 frames for T1data.
 17. A system according to claim 7, further including a switch forreceiving (i) the parameter k from the processor, (ii) a user-definedparameter k, and (iii) a switch control signal, wherein the switchprovides, to the packet assembler, either the parameter k from theprocessor or the user-defined parameter k, as a function of the switchcontrol signal.